In optical communications networks, optical transceiver modules are used to transmit and receive optical signals over optical fibers. An optical transceiver module generates modulated optical signals that represent data, which are then transmitted over an optical fiber coupled to the transceiver module. Each transceiver module includes a transmitter side and a receiver side. On the transmitter side, a laser light source generates laser light and an optical coupling system receives the laser light and optically couples the light onto an end of an optical fiber. The laser light source typically is made up of one or more laser diodes that generate light of a particular wavelength or wavelength range. The optical coupling system typically includes one or more reflective elements, one or more refractive elements and/or one or more diffractive elements. On the receiver side, a photodiode detects an optical data signal transmitted over an optical fiber and converts the optical data signal into an electrical signal, which is then amplified and processed by electrical circuitry of the receiver side to recover the data. The combination of the optical transceiver modules connected on each end of the optical fiber and the optical fiber itself is commonly referred to as an optical fiber link.
In switching systems that are commonly used in optical communications networks, each optical transceiver module is typically mounted on a circuit board that is interconnected with another circuit board that is part of a backplane of the switching system. The backplane typically includes many circuit boards that are electrically interconnected with one another. In many such switching systems, each circuit board of the backplane has an application specific integrated circuit (ASIC) mounted on it and electrically connected to it. Each ASIC is electrically interconnected with a respective optical transceiver module via electrically-conductive traces of the respective circuit boards. In the transmit direction, each ASIC communicates electrical data signals to its respective optical transceiver module, which then converts the electrical data signals into respective optical data signals for transmission over the optical fibers that are connected to the optical transceiver module. In the receive direction, the optical transceiver module receives optical data signals coupled into the module from respective optical fibers connected to the module and converts the respective optical data signals into respective electrical data signals. The electrical data signals are then output from the module and are received at respective inputs of the ASIC, which then processes the electrical data signals. The electrical interconnections on the circuit boards that connect inputs and outputs of each ASIC to outputs and inputs, respectively, of each respective optical transceiver module are typically referred to as lanes.
FIG. 1 illustrates a block diagram of a known optical communications system 2. The optical communications system 2 comprises a first circuit board 3, an optical transceiver module 4 mounted on the first circuit board 3, a backplane circuit board 5, and an ASIC 6 mounted on the backplane circuit board 5. Four output optical fibers 7 and four input optical fibers 8 are connected to the optical transceiver module 4. In the transmit direction, the ASIC 6 produces four electrical data signals, which are output from the ASIC 6 onto four respective output lanes 9 to the optical transceiver module 4. The optical transceiver module 4 then converts the four electrical data signals into four respective optical data signals and couples them into the ends of four respective optical fibers 7 for transmission over the optical fiber link. In the receive direction, four optical data signals are coupled from the ends of four respective optical fibers 8 into the optical transceiver module 4, which then converts the optical data signals into four electrical data signals. The four electrical data signals are then output over four respective input lanes 11 to four respective inputs of the ASIC 6 for processing by the ASIC 6. Each of the electrical data signals and optical data signals are operative at a data rate of 10 Gbps. Thus, the optical fiber link, with four data channels of 10 Gbps each in the transmit direction, has a transmit data rate of 40 Gbps. Similarly, the optical fiber link, with four data channels of 10 Gbps each in the receive direction, has a receive data rate of 40 Gbps. The data rate of the optical fiber link can be increased by increasing the number of optical transceiver modules 4 and ASICs 6 that are included in the link. For example, if four optical transceiver modules 4 and four ASICs 6 are included in the optical communications system 2, the optical fiber link will have a data rate of 160 Gbps in the transmit direction and 160 Gbps in the receive direction.
Ever-increasing demands for greater bandwidth often lead to efforts to upgrade optical fiber links to achieve higher data rates. Doing so, however, typically requires either duplicating the number of optical transceiver modules and ASICs that are used in the optical communications system, as described above, or replacing the optical transceiver modules and ASICs with optical transceivers and ASICs that operate at higher data rates. Of course, duplicating the number of optical transceiver modules and ASICs that are used in the optical communications system increases the cost associated with providing and operating such a solution. Similarly, it is desirable to avoid costs associated with developing and providing ASICs that operate at higher data rates. Consequently, it is desirable to provide a way to substantially increase the bandwidth of an optical fiber link without having to duplicate the number of optical transceiver modules and ASICs that are employed in the optical communications system.
Another approach to increase the bandwidth of a communication link is to combine two or more data channels prior to transmission. Such implementations are complicated for at least the reason that the two or more data channels should be synchronized before they can be combined. One conventional approach to synchronizing serial data channels involves delaying a first data channel to align the data signal therein with a respective data signal in a second data channel. While the insertion of static delays in a data channel is desirable for its low power consumption and relatively small circuit area footprint requirements, this approach has a limited compensation range that make it unsuitable for relatively large data signal skews. A second conventional approach to synchronizing serial data channels involves adjusting the incoming data rate and buffering the reduced rate data channels with an elastic first-in first-out (FIFO) buffer. The elastic FIFO is used to adjust the data based on a divided clock from a clock and data recovery circuit before the FIFO outputs are combined. While this second conventional approach is capable of correcting a relatively larger range of dynamic skew between the data channels, the additional circuitry adds significantly to the circuit area required and increases overhead power consumption.
Accordingly, it would be desirable to provide a way to upgrade a communication link to achieve higher data rates without having to duplicate the number of optical transceiver modules and ASICs that are employed in the optical communications system and without having to redesign the ASIC.